Physiology Chp 10 Part B PDF

Physiology: Chp 10 Part B Central Nervous System Juan J. Bustamante, Ph.D. Assistant Professor Pharmaceutical Science Phone (361) 221-0643 Email: [email protected] Office: Room 223 © 2016 Pearson Education, Inc.  Properties of Stimulus: I...

Physiology: Chp 10 Part B Central Nervous System Juan J. Bustamante, Ph.D. Assistant Professor Pharmaceutical Science Phone (361) 221-0643 Email: [email protected] Office: Room 223 © 2016 Pearson Education, Inc.  Properties of Stimulus: Intensity and Duration Intensity – Coded by number of receptors activated and frequency of action potentials called frequency coding Duration – Coded by duration of action potentials – Some receptors can adapt, or cease to respond Tonic receptors versus phasic receptors © 2016 Pearson Education, Inc. Figure 10.6 Coding for stimulus intensity and duration Cell body Axon terminal Transduction site Trigger zone Myelinated axon Stimulus Moderate Stimulus Membrane potential (mV) 20 0 Amplitude −20 −40 Threshold −60 −80 0 5 10 0 5 10 0 5 10 Duration Time (sec) Membrane potential (mV) Longer and 20 Stronger Stimulus 0 −20 −40 −60 −80 0 5 10 0 5 10 0 5 10 Frequency of action Receptor potential Receptor potential Neurotransmitter potentials is proportional strength and is integrated at the release varies to stimulus intensity. duration vary with trigger zone. with the pattern Duration of a series of the stimulus. of action potentials action potentials is arriving at the axon proportional to stimulus terminal. duration. © 2016 Pearson Education, Inc. Figure 10.7a Receptor adaptation In general, the stimuli that activate tonic receptors are parameters that must be monitored continuously by the body such as baroreceptor. © 2016 Pearson Education, Inc. Figure 10.7b Receptor adaptation This type of response allow the body to ignore information that have evaluated and found not to threaten homeostasis or well-being for example smell – cologne © 2016 Pearson Education, Inc.  Somatic Senses: Modalities Touch Proprioception Temperature Nociception – Pain – Itch © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 1 Sensations are perceived in the primary somatic sensory cortex. KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron Sensory pathways synapse in the THALAMUS thalamus. MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 2 KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron THALAMUS MEDULLA Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 3 KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron THALAMUS MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 4 KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron Sensory pathways synapse in the THALAMUS thalamus. MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 5 Sensations are perceived in the primary somatic sensory cortex. KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron Sensory pathways synapse in the THALAMUS thalamus. MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.9 The somatosensory cortex No pain fiber in the brain The amount of space Posterior on the somatosensory view cortex devoted to Size of region not fix. each body part is proportional to the sensitivity of that part. Reading braille enlarge region devoted to fingertips Lost of a finger – area take over by adjacent structure Thalamus Cross section of the right cerebral hemisphere and sensory areas of the Sensory signals cerebral cortex from left side of body © 2016 Pearson Education, Inc. Figure 10.10-1 Sensory receptors in the skin Merkel receptors Meissner's corpuscle sense steady pressure responds to flutter and and texture. stroking movements. Hair Free nerve ending Free nerve ending of Free nerve ending nociceptor responds of hair root senses Hair root to noxious stimuli. hair movement. Sensory nerves Pacinian corpuscle carry signals to senses vibration. spinal cord. Ruffini corpuscle responds to skin stretch. © 2016 Pearson Education, Inc.  Temperature Receptors Free nerve endings Terminate in subcutaneous layers Cold receptors – Lower than body temperature Warm receptors – Above body temperature to about 45°C – Pain receptors activated above 45°C © 2016 Pearson Education, Inc.  Nociceptors Nociceptors are neurons that respond to a variety of strong noxious stimuli (chemical, mechanical, or thermal) that cause or have a potential to cause tissue damage. Nociceptors are found in skin, joints, muscle, bones, and various internal organ, but not in the central nervous system. Activation of nociceptor pathways initiates adaptive, protective responses. Example: When you fell pain you stop or you run away. © 2016 Pearson Education, Inc.  Nociceptors Respond to strong noxious stimulus that may damage tissue Free nerve endings Afferent signals from nociceptors are carried to the CNS in two types of primary sensory fibers 1. Aδ fibers 2. C fibers © 2016 Pearson Education, Inc.  Nociceptors Pain – most common sensation carried by these pathways Subjective perception –pain is highly individual and multidimensional, may vary with person’s emotional state. © 2016 Pearson Education, Inc.  Nociceptors Fast pain Sharp and localized—by Aδ fiber Slow pain Duller and more diffuse—by C fibers  Nociceptors The timing distinction between the two is most obvious when the stimulus originates far from the CNS, such as when you stub your toe. You first experience a quick stabbing sensation (fast pain), followed shortly by a dull throbbing (slow pain) Itch – Histamine activates C fibers, causing itch © 2016 Pearson Education, Inc.  Nociceptors Pathways The primary sensory neurons from the nociceptor terminate in the dorsal horn of the spinal cord. Nociceptor activation can follow two pathways Reflexive protective response – Integrated in spinal cord – Withdrawal reflex – hot stove (unconscious) Ascending pathway to cerebral cortex – Becomes conscious sensation (pain or itch) © 2016 Pearson Education, Inc. Figure 9.7 Spinal reflexes Reflexive protective response – Integrated in spinal cord – Withdrawal reflex – hot stove (unconscious) Afferent neurons connect with interneurons in the dorsal horns © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 5 Ascending pathway to cerebral cortex – Becomes conscious sensation (pain or itch) The pathways also send branches to the limbic system and hypothalamus. © 2016 Pearson Education, Inc.  Nociceptors Pathways The following increase sensitivity to pain (activate nociceptors) at a site of tissue damage is call inflammatory pain. – Substance P is secreted by primary sensory neurons – Mediate inflammatory response –damaged cells release K+, histamine, and prostaglandins Ischemia is lack of adequate blood flow Chronic pain is a pathological (neuropathic) pain – damage © 2016 Pearson Education, Inc. Figure 10.11a Referred pain Pain in internal organs is often sensed on the surface of the body, a sensation known as referred pain. Heart Liver and gallbladder Stomach Small intestine Ureters Appendix Colon © 2016 Pearson Education, Inc. Figure 10.11b Referred pain © 2016 Pearson Education, Inc.  Pain Modulation Why can we ignore/suppress pain? Gate control theory: Aβ fibers synapse on inhibitory interneurons and increase inhibition – Integrated response from Aβ and C fibers decreases the perception of pain. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. Figure 10.12a The gate control model © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc.  Pain Modulation Analgesic drugs – Aspirin (NSAID; nonsteroidal anti-inflammatory drug Inhibits prostaglandins, decreases inflammation, and slows transmission of pain to site of injury – Opioids Block pain perception by decreasing primary sensory neuron neurotransmitter release and by postsynaptic inhibition of secondary sensory neurons Endogenous opioids: Endorphins, enkephalins, dynorphins Drugs – develop tolerance © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 5 Ascending pathway to cerebral cortex – Becomes conscious sensation (pain or itch) The pathways also send branches to the limbic system and hypothalamus. © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. Aspirin: Low Dose Aspirin: High Dose © 2016 Pearson Education, Inc.